1. Field of the Invention
The present invention relates to a vehicle roof mount antenna detachably mounted on a vehicle roof, and more particularly to a vehicle roof mount antenna improving waterproofness and dustproofness.
2. Description of the Related Art
A vehicle roof mount antenna typically has a pad on a contact surface with a vehicle roof. The pad has an annular rib (flange) made of an elastic material so as to improve waterproofness and dustproofness. The installation pressure of a boss brings the annular rib of the pad into press contact with the vehicle roof, thereby ensuring the waterproofness and dustproofness of the vehicle roof mount antenna.
For example, Patent Document 1 (Japanese Patent Application Kokai Publication No. 2005-102031) discloses an antenna for an automobile. The antenna has a pad in which a plurality of substantially triangular-shaped ribs are provided for waterproofness and thereby prevents entering of rain water and the like.
In such a vehicle roof mount antenna using a pad having an annular rib, when the installation pressure is used to bring the annular rib into press contact with the vehicle roof, the annular rib is deformed to be tightly attached to the vehicle roof. At this time, a pressing force corresponding to the deformation amount is given to the vehicle roof. When the pressing force is excessively large, a problem that the vehicle roof is deformed arises. Further, when the installation pressure of the boss is reduced so as not to cause the deformation of the vehicle roof, the waterproofness and the dustproofness which are the intended functions of the annular rib cannot be ensured satisfactorily.
Recently, a reduction in the weight of a vehicle body is now an important trend, and along with the weight reduction, the thickness of the vehicle roof has been reduced. Therefore, the problem of the deformation of the vehicle roof has become more prominent.
The vehicle roof typically has a slight curved surface shape, so that the deformation amount of the annular rib may become nonuniform throughout the entire circumference of the annular rib at some position on which the vehicle roof mount antenna is mounted. In particular, there is a gap between the annular rib that is away from the boss and the vehicle roof, so that satisfactory waterproofness and dustproofness cannot be ensured.
An object of the present invention, therefore, is to overcome the problems existing in the prior art, and to provide a roof mount antenna device which does not cause a vehicle roof to be deformed even when the vehicle roof on which the roof mount antenna device is mounted has a small thickness and which is capable of ensuring satisfactory waterproofness and dustproofness even when the vehicle roof on which the roof mount antenna device is mounted has a curved surface shape.